It's almost certainly memory related. That doesn't necessarily mean the memory is faulty. I have built a lot of shuttles over the last few years, and quite frequently I have seen similar results which were resolved by using different memory, while the stick taken from the apparently faulty shuttle worked fine in another machine. Shuttle motherboards seem to be particularly picky about which ram will work correctly with them. Switching to Crucial (micron) ram fixed the problem.

Memory faults or errors can give very odd diagnostics in some machines. A friend's company was having major problems with installing 2000 on a whole series of identical machines, where it was giving hard drive and/or CD read errors. The symptoms were similar to the ones you're reporting. It turned out that by swapping the ram sticks around between the machines you could fix the faulty hard drive The timings on the memory/motherboard combination were just too close to the edge to be reliable.

pca